The present invention generally relates to force sensing and, more particularly to a force sensing system.
Various automated manufacturing activities require precise placement and/or grasping of objects, in which contact forces between a manipulator (or other article contacting mechanism) and an object are at a minimum. Many of these activities may be performed by industrial robots having a mechanism for picking-up and placing objects, such as in semiconductor chip manufacturing processes as well as other types of force controlled placement systems.
When an object-receiving feature, for example, contacts an object that is to be moved, there are impact forces between the feature and the object. In order to mitigate the impact forces, the movement of the receiving feature may be controlled, such as based on sensing the impact force.
A typical force sensing system may employ a strain gauge or load cell that that senses forces applied to an associated receiving feature. In one particular application, a spring may be employed to preload a load cell. A spring, however, has memory (e.g., it elastically deforms) and, thus, tends not to return fully to its original configuration after repeated stress. Because of its elastic deformation, a spring tends to degrade over time, changing the preloading characteristics of the associated load cell. This decreases the level of precision in the load cell. A spring also may exhibit resonance as it is loaded and unloaded. The resonance of the spring may, in turn, increase the acquisition cycle time, as the oscillations need time to subside between measurement intervals. Therefore, the overall throughput of an entire system may be adversely affected by the spring.
The present invention provides for a force sensing system, which may be employed in a manufacturing environment to sense impact force between a feature and an object for example. The subject invention mitigates some of the problems associated with many convention force sensing systems (e.g., spring based systems) which have issues of system degradation and relatively poor cycle time (due to spring resonance), the present invention. By employing a pair of opposing magnetic elements in connection with preloading a force sensor, a force sensing system results which is less prone to system degradation because magnetic elements in accordance with the present invention do not substantially degrade with respect to their magnetic properties. Furthermore, the present invention results in improved cycle time/throughput as compared to spring based systems because the opposing magnets of the present invention damp relatively quickly as compared to many of the conventional systems which are susceptible to spring resonance.
One aspect of present invention relates to a force sensing system that includes a pair of magnets for preloading a force sensor. A first magnet is spaced apart from the force sensor, with the second magnet being located between the first magnet and the force sensor. The magnets are arranged so that sides of each magnet having like polarity face each other (e.g., the magnets repel each other). The second magnet is operatively associated with the force sensor to preload the force sensor based on repulsive forces generated by the first and second magnets. The distance between the magnets, thus, may be controlled to preload the force sensor to a desired amount. The magnetic characteristics of the magnets remain substantially unchanged over time, thereby mitigating system degradation. Additionally, the opposed magnets provide a stiffened response with minimal resonance, thus, permitting faster recovery and increased throughput with the system in accordance with the present invention.
Another aspect of the present invention provides a force sensing system. The system includes a first magnet having a first polarity on a first side and a second polarity on a second side opposite the first side thereof. A second magnet has the first polarity on a first side and the second polarity on a second side opposite the first side thereof. The system also includes a force sensor spaced apart from the first magnet. The second magnet is interposed between the force sensor and the first magnet and the second side of the second magnet faces the second side of the first magnet. The second magnet preloads the force sensor based on interactions between magnetic fields of the first and second magnets.
Another aspect of the present invention provides a force sensing system. The system includes a housing having first and second ends that are spaced apart from each other and a central axis extending through the first and second ends. A force receiving member has a first portion located within the housing substantially transverse relative to the central axis and a second portion extending from a central part of the first portion axially through an aperture in the first end of the housing. A force sensor is located intermediate the first end of the housing and the first portion of the force receiving member. The force sensor has an aperture extending axially through a central part of the force sensor through which the second portion of the force receiving member extends. The force sensor is operative to sense force as a function of position of the force receiving member relative to the housing and the force sensor.
Yet another aspect of the present invention provides a force sensing system. The system includes a pair of opposed magnets spaced apart from and arranged relative to each other so as to repel each other and generate a repulsive force. A force sensor is operatively associated with one magnet of the pair of magnets. The one magnet preloads the force sensor according to the repulsive force of the first and second magnets.
Still another aspect of the present invention provides a force sensing system. The system includes force sensing means for sensing an applied force and magnetic means for preloading the force sensing means. The preloading of the force sensing means varies by an amount functionally related to the applied force.
To the accomplishment of the foregoing and related ends, certain illustrative aspects of the invention are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.